The present invention relates to devices for temporarily shutting off conduits, of the kind comprising a flexible sleeve expansible under powerful internal pressure, having a rubber wall which is reinforced by at least two pairs of superimposed plies of cords defining an internal tube and an external sheath, the cords of all the plies being crossed from one ply to the other whilst forming angles smaller than 30.degree. with respect to the generatrices. Hereinafter such devices will be referred to as "of the kind described". They are used inter alia for temporarily shutting off conduits which are to be repaired, bore holes or injection holes in rock.
Shut-off devices of the kind described are already known, comprising an expansible element formed by a portion of rubber tube or sleeve secured at each end to connectors of which at least one is connected to a source of pressurised liquid rendering it possible to expand the sleeve. The wall of the sleeve is reinforced by pairs of plies of metal strands crossed from one ply to another and forming with the generatrices smaller angles than the pressure balance angle which amounts to approximately 54.degree.. These known devices are satisfactory up to already very high pressures in application, of the order of 200 to 250 bars. There are applications however which have not been implemented until now, in which it would be necessary to be able to utilise these devices at even higher pressures, for example up to 550 bars and more, to be able to balance pressures from 300 to 500 bars prevailing in particular conduits or bore holes which are to be plugged, with sufficient reliability. Since it is undesirable to multiply the number of pairs of plies of cord reinforcements at the cost of reducing the capacity of expansion of the tube, users are compelled to make use of no more than a single pair of thicker stranded cords to obtain the desirable theoretical strength. It is then observed however that with these thick cords, the rubber of the tube wall in which they are embedded is impelled into the gaps between the cords when the device is exposed to extremely high inflation pressures.
It is an object to mitigate this disadvantage.